1. Technical Field
The present invention generally relates to a shovel including an electrical energy storage device composed of multiple electrical energy storage cells and a method of controlling such a shovel.
2. Description of Related Art
Shovels according to related art include an electrical energy storage unit that includes multiple electric double-layer capacitors (cells) connected in series and equalizer circuits provided one for each of the cells.
The equalizer circuits according to related art each determine whether the voltage across a corresponding cell (cell voltage) is higher than or equal to an operating voltage by dividing the cell voltage using resistors and detecting a fraction of the cell voltage with a detecting element, and turn on a semiconductor switch to cause an electric current to leak through a bypass circuit when the cell voltage is higher than or equal to the operating voltage.
Thus, the equalizer circuits according to related art prevent the cell voltage of each cell from exceeding the operating voltage by individually discharging cells whose cell voltage is higher than or equal to the operating voltage, so as to maintain the cell voltage of each cell within a fixed range and to keep the cell voltages of the cells equal.